1. Field of the Invention
The present invention relates to an ophthalmic apparatus such as an eye-refractometer used in an ophthalmic hospital.
2. Related Background Art
A prior art ophthalmic apparatus such as an eye-refractometer has a diopter inducing optical system to induce a refractive power of an eye under test to a far point by changing the diopter of a target in order to permit accurate measurement. In such an apparatus, the position of the target is always constant prior to the inducement and a standard diopter of the diopter inducing system is set to essentially fit to a emmetropic eye.
However, in the prior art apparatus, if the eye under test is emmetropic, it can easily recognize the initially set target and the inducement can be immediately started, but if the eye under test is myopic or hyperopic, it is hard to recognize the target. Accordingly it is necessary to first measure, the refractive power of the eye and reinitialize the diopter of the target based on the refractive power of the eye. Thus, a time band during which the eye under test cannot clearly recognize the target is included and the measurement time is long.
U.S. Pat. No. 4,929,076 discloses the adjustment of the diopter of a fixed target when the curvature of a cornea is measured, in accordance with the measurement of the refractive power of the eye but it is different from the idea of this invention of eliminating the time band during which the eye under test cannot clearly recognize the fixation target in the initial stage of the measurement.
In the past, the refractive power of an eye-glass lens and a refractive power of an eye have been sequentially measured by separate apparatus in an eye-glass shop. Thus, if the eye under test has myopia or is hyperopic, a time band during which the eye under test cannot clearly recognize the fixation target is included in the initial stage of the measurement of a refractive power of the eye.